Electric utilities are the largest provider of energy to industrial, commercial and residential consumers. The infrastructure used to support the delivery of energy to the more than 100 million customers in the U.S. has been evolving for over 100 years. The electric power network or “power grid” is comprised of power generation systems, which are connected by an electricity transmission network to an electricity distribution network. Power generation systems typically include power plants, where electricity is generated by electromechanical generators driven by engines fueled by a form of combustion, or by some kinetic energy, such as water or wind. Alternative energy sources of power generation, such as photovoltaic or solar heat panels are also commonly connected to the power grid.
The electricity transmission network transfers bulk electricity originating from the power generating plants to local substations that are closer to electricity demand centers. The transmission network transmits electric power at high voltages, generally along overhead power lines. The high voltage transmission reduces the energy lost while in transit. Important components of the transmission system include electric conductors, structural support, and accessory elements, such as transformers, switches and insulators. Finally, the electrical transmission system or network connects to the electrical distribution network, which delivers electrical energy to the end-user or consumer.
The electrical distribution system transmits power from local substations to local consumers at lower voltages than the transmission network. The distribution network is commonly made up of 20 to 40-foot wooden or steel poles, which support and suspend power lines or conductors, disconnect devices, lightning arresters, capacitors, insulators, and a variety of pole line hardware elements. Power lines running between power poles are commonly referred to as “overhead lines.” Distribution of electric power through underground power lines has also become increasingly common in recent years, though it can present substantial increases in cost beyond that of overhead lines. Together, the power generation system, and transmission and distribution networks, instantly deliver energy to all customers on an on-demand basis, allowing the myriad of electrically-powered products and services to be routinely utilized.
In certain situations, environmental, cosmic, or physical intervention against electric transmission or distribution structures has caused significant power outages, and for some specific events, these outages have been geographically extensive and caused outages of much longer than a few hours. On Aug. 14, 2003, a series of failures of electrical systems in the northeastern United States and the Canadian province of Ontario caused a large-scale blackout that knocked out power to more than 55 million people. At the time, the blackout was the largest in history, with more total wattage and more individuals affected by the blackout than any other previous outage. The blackout was caused primarily by computer and alert system failures, which permitted surges along overhead transmission lines in Ohio to occur, causing several transmission lines short after contacting trees or other foreign objects, leading to further cascading outages. A joint American-Canadian task force that was established to investigate the causes of the blackout pointed to the deteriorating condition of a major electric utility's system as one of the primary causes of the blackout. The event showed the importance of carefully monitoring and maintaining weak and vulnerable points in the electric grid.
Weather events can cause widespread damage, and knowledge of the condition of individual structures can be useful for avoiding outages, and for planning repairs. In 1998, an ice storm caused the collapse of hundreds of electric transmission towers in Quebec, Canada, while some parallel lines survived. In such emergencies full knowledge of the condition of individual towers would allow for an improved response by technicians. In the 1998 event, over one million customers (about half the population of Quebec) were left powerless, as a result of damage to more than 100 high voltage transmission lines and the collapse of over 3,000 transmission towers. Similarly, the electric distribution system was damaged including more than 300 damaged lines and 10,000 collapsed structures. Similar events are not rare, and information of the integrity of grid structures is essential for a measured response.
In a 2007 weather event, an ice storm affecting Kansas caused more than $100 million of damage to the power infrastructure, involving about 2,000 power poles, 8,000 spans of power conductor and re-fusing of about 5,000 lines and transformers.
In diverse regions affected by war and internal conflict, attacks on electricity transmission structures have resulted in extensive power outages. During the 1980's, anti-Soviet Afghan insurgents were paid to attack an electricity transmission line extending from Sorubi to Kabul. In a very short period of time, many transmission towers were demolished. The dispersed structures of the transmission line system were left unprotected and subject to vandalism.
Decades later the USAID invested $355 million on the “Tarakhil Power Plan” to improve stability of the Afghan power grid. In January 2016, a transmission line supplying electricity to Kabul, Afghanistan from neighboring Uzbekistan was attacked by insurgents. Insurgents destroyed a single transmission tower and damaged others that were located near a highway in a rural area in Baglan province. The result was a day long power outage in the populated Kabul region. Repair attempts were begun soon after, but were hampered by anti-personnel mines left behind by the insurgents. Electricity service was disrupted for weeks. The stability and safety of the electric power grid could be substantially improved by increasing the knowledge about transmission system condition and improved security to maintain integrity.
The distribution network or system is a single path for the delivery of energy to homes, businesses, and industry. It begins at the step-down transformer at a substation. The step-down transformer reduces the voltage of the circuit from transmission levels to lower distribution voltages. An involved conductor or conductors in the entire network is energized to the particular distribution voltage level to the connection with the distribution transformer which reduces the voltage once more to the appropriate low delivery voltage. For example, a typical home usually receives a voltage of 120 volts line to neutral or 240 volts line to line.
The electricity distribution network is increasingly separated from the electric power generation system. In most locations, electricity distribution is a regulated public utility. Distribution voltages are generally standardized at various levels, including, for instance, 69 kV, 34.5 kV, 17.2 kV, 12 kV, 7.2 kV, 4.7 kV, and 2.7 kV. These voltages are transformed near the location of consumption to 480, 240, and 120 volts for use in machinery, systems, and homes. The distribution system or network is made up of 20- to 40-foot wooden or steel poles from which are suspended power lines or conductors, disconnect devices, lightning arrestors, capacitors, insulators, and a variety of pole line hardware elements, each of which plays a crucial role in keeping the lights on and factories running.
Substations contain step-down transformers that reduce the voltage of the circuit from transmission levels to lower distribution levels. The transformers, insulators, lightning arresters, capacitors, wires, poles, and other parts of the electric grid must all work properly and in unison for consistent electric power to consumers to be maintained. Consistent power supply quality and levels requires efficient coordination between all elements of the system. Minor damage or deterioration to even seemingly small parts can have major consequences throughout an electric power grid. Power lines supported by power poles are referred to as overhead lines. The active function of the electrical system or network is defined and limited directly by the reliability of the multitude of components. There is a continuing need to provide relevant information on grid status while there is still sufficient time available for technicians to take appropriate action.
There are over three million miles of overhead and underground electrical distribution circuits in the U.S. that provide consumers access to electrical energy. Ninety percent of all interruptions to electrical service occur when elements of the distribution system break down. The distribution system is the delivery point for all utility customers, except for the largest industrial customers such as steel mills and automotive manufacturing plants. Large industrial customers purchase energy on a wholesale basis at transmission voltage levels of 138 kV, 230 kV, 345 kV, 500 kV, or 765 kV. These wholesale customers include other utilities that buy and sell power on the wholesale market.
If any of the hardware connecting, insulating, or protecting the distribution circuit or system fails, all of the loads downstream of the failure become affected. Sometimes a power outage occurs because there has been a problem such as a tree limb falling across a line or an animal causing an electrical fault by bridging across two conductors. However, equipment or component failure is the leading cause of distribution circuit failure. When an equipment or component failure occurs, the broken element must be located and replaced.
One type of equipment or component failure that is often a problem is the structures supporting conductors and other electric utility equipment. In particular at risk are electricity transmission conductor support towers. The towers supporting the highest voltage conductors are typically constructed from structural steel, and particularly structural steel shapes that are welded, bolted or riveted together. One problem with monitoring transmission tower integrity is that there are a wide variety of structural designs. Common tower designs include free standing multiple element trusses, and single or multiple beam towers supported by guy lines. Within the structural steel tower category, there is a wide variety of individual designs.
In addition there are towers constructed of metal tubes, i.e. steel or in certain instances of steel reinforced concrete. Wood poles oftentimes include a ground or lightning arrestor cable that functions as a conductor element.
Detecting incipient failures of the entire system, including transmission and distribution structural elements is important for maintaining grid reliability. The structural elements may suffer from fatigue, corrosion, wind induced stress, impact damage, vandalism or even intentional unauthorized disassembly. Each of these or other foreseen or unforeseen insults to the structures supporting the structural elements of the electric grid may lead to local or widespread power outages. It would be very useful to remotely or continuously monitor the condition of these structural elements.
Identifying potential failures in conductors varies with differing types of conductors, and the power carried by those systems. Underground 120/277 volt, AC, 60 Hz network cable and associated terminations and hardware are designed to be buried underground, in or out of a conduit. Jacketed LV type underground cable is typically comprised of a stranded copper core of 10-30 individual wire conductors, surrounded by an insulating layer, and covered with an impervious protective sheath.
A variety of systems involved in energy delivery utilize components that are capable of conducting electricity or responding to an electrical current, RF field, or inductive field. These systems, such as gas and oil pipelines are difficult to remotely monitor, and are also potentially highly hazardous if a failure incident should occur.
Currently available monitoring products have a relatively high base cost and require technical skill, devoted labor, and post-analysis to be effective. In addition, the effectiveness of these products also relies on the opportunistic discovery of an already failing circuit or structural element. Developing a system that allows for accurate and cost-effective predictive maintenance would be extremely beneficial to utility companies or other entities that conduct maintenance of electrical systems. Predicting and targeting system weaknesses before they can lead to major failures can help to reduce outages caused by deteriorated system components, and in turn likely reduce the chances of large scale blackouts caused by vulnerabilities in electrical grid components.